So, here you go: The 13 Most Successful (Secular) Novels Never to Be Adapted Into a Feature Film. Note that The Hobbit would top this list, but I left it off because the feature film is well into development.

13. Things Fall Apart by Chinua Achebe (11 million copies sold)

12. Tuesdays with Morrie by Mitch Albom (14 million copies sold) (Note: There has been a TV movie.)

11. The Shadow of the Wind by Carlos Ruiz Zafon (15 million copies sold)

10. The Pillars of Earth by Ken Follett (15 million copies) (A TV mini-series is in the works.)